The present invention relates to the testing and maintenance of semiconductor processing equipment. The present invention especially relates to the testing and maintenance of etching devices.
Etchers such as LAM Research 9600 available from the LAM Research Corporation of Fremont, Calif., use a wafer clamp to hold a wafer in position during processing. FIG. 1 is a partial cross-sectional view of prior etcher 10, including a wafer clamp 12, wafer 14, and bottom electrode 16. This diagram exaggerates the curvature of the bottom electrode 16 and is not to scale. The wafer 14 is positioned in the etcher by a robotic handler (not shown). The wafer clamp 12 comes down and holds the wafer 14 against the bottom electrode 16. An overlap 18 between the wafer clamp 12 and the wafer 14 is usually kept relatively small so that the largest possible area of the wafer 14 is available to be processed. In etchers such as the LAM Research 9600 series, helium gas flows around the back side of the wafer 14 to cool the wafer 14 during the etching.
One problem that has occurred during processing is that the photoresist on the wafer 14 can melt when excess heat accumulates on the wafer 14. Melted photoresist will prevent the circuit pattern from being accurately etched onto the wafer 14. This will cause the failure of the wafer 14. Failure caused by melted photoresist is not immediately noticeable; the wafer 14 will go through additional processing steps and other wafers will be improperly processed in the etcher. The damaged wafers and wasted processing time can produce a considerable expense.
There is thus a need for a better approach for evaluating the extent of wear of a wafer clamp that is more reliable and less cumbersome.